Modern high definition (high resolution) television projectors, video wall projection engines, and rear-projection engines in general commonly employ a single lens for projecting the three primary colors of an image toward a viewing screen. Projection optics focus the images in three primary colors upon a viewing screen that typically includes a single layer of transparent microspheres contiguously oriented on a side of the viewing screen opposite the side facing a viewer.
In such image projection systems there commonly appear on the viewing screen tiny regions of visually distinctive image intensity well above or well below the average intensities of the projected image (referred to herein as ‘speckles’). Such speckles of high and low image intensity are substantially high spatial frequency optical noise believed to be caused by interference of partially coherent projected light rays or waves. These speckles appear to flicker or move with changes in viewing angle and are objectionable characteristics that are to be minimized and eliminated.
There is an additional component of this high frequency noise that appears static, and does not appear to shimmer or flicker with changes in viewing angle. These tiny regions of high and low intensity light can be clearly distinguishable from speckle. These tiny static regions of high and low light intensity are termed “screen grain or graininess,” and are believed to be caused by uneven penetration through the thin black layer by the optical beads that comprise the beaded screen. The uneven penetration of beads causes smaller or larger apertures for image light to pass to the viewing screen. These regions are also objectionable to viewers and are to be minimized or eliminated.